I have never understood this. Do other gyms athletes have to get their own chalk?
At our gym the chalk is bought by the gym and kept at the gym, everybody shares that nobody ever has their own in their bag.
My first thought was, in the giant orange Home Depot bucket. And then I read Tupperware container and could just picture the mess of several little girls trying to use chalk out of that! Gyms in the US provide it for all members of the gym. If I had to provide my own, though, I would look for a tight container with a locking top, something like this: http://www.amazon.com/gp/aw/d/B001AZNAWY. I think that would help prevent spilling.
All the gymnasts bring their own chalk to our gym. As Margo says, it's a little block about 5"x3"x2" and fits neatly in a tupperware tub with a snaplock lid. Lasts for months and doesn't seem to make any mess.
The gym does leave a couple of little blocks in the beam area, used for marking where to start dismounts etc.
at the gym we supply the chalk but when we are at meets they sometimes are low or stingy and there is no chalk by the beam. We bought a chalk ball. I think ten-o sells them. It is chalk that is put in a cheese cloth like stocking and it works well at keeping the mess down